852 research outputs found
Green's Function Zeros in Fermi Surface Symmetric Mass Generation
The Fermi surface symmetric mass generation (SMG) is an intrinsically
interaction-driven mechanism that opens an excitation gap on the Fermi surface
without invoking symmetry-breaking or topological order. We explore this
phenomenon within a bilayer square lattice model of spin-1/2 fermions, where
the system can be tuned from a metallic Fermi liquid phase to a
strongly-interacting SMG insulator phase by an inter-layer spin-spin
interaction. The SMG insulator preserves all symmetries and has no mean-field
interpretation at the single-particle level. It is characterized by zeros in
the fermion Green's function, which encapsulate the same Fermi volume in
momentum space as the original Fermi surface, a feature mandated by the
Luttinger theorem. Utilizing both numerical and field-theoretical methods, we
provide compelling evidence for these Green's function zeros across both strong
and weak coupling regimes of the SMG phase. Our findings highlight the
robustness of the zero Fermi surface, which offers promising avenues for
experimental identification of SMG insulators through spectroscopy experiments
despite potential spectral broadening from noise or dissipation.Comment: 12 pages, 7 figures. 1 appendi
Definition and Classification of Fermi Surface Anomalies
We propose that the Fermi surface anomaly of symmetry group in any
dimension is universally classified by -symmetric interacting fermionic
symmetry-protected topological (SPT) phases in -dimensional spacetime.
The argument is based on the perspective that the gapless fermions on the Fermi
surface can be viewed as the topological boundary modes of Chern insulators in
the phase space (position-momentum space). Given the non-commutative nature of
the phase space coordinates, we show that the momentum space dimensions should
be counted as negative dimensions for SPT classification purposes. Therefore,
the classification of phase-space Chern insulators (or, more generally
fermionic SPT phases) always reduces to a -dimensional problem, which
can then be answered by the cobordism approach. In addition to the
codimension-1 Fermi surface case, we also discuss the codimension- Fermi
surface case briefly. We provide concrete examples to demonstrate the validity
of our classification scheme, and make connections to the recent development of
Fermi surface symmetric mass generation.Comment: 13 pages + references, 2 figures, 2 tables. Update Tab. II,
clarifications to codimension-p Fermi surface, and references adde
Emergent self-duality in long range critical spin chain: from deconfined criticality to first order transition
Over the past few decades, tremendous efforts have been devoted to
understanding self-duality at the quantum critical point, which enlarges the
global symmetry and constrains the dynamics. In this letter, we employ
large-scale density matrix renormalization group simulations to investigate the
critical spin chain with long-range interaction .
Remarkably, we reveal that the long-range interaction drives the deconfined
criticality towards a first-order phase transition as decreases. More
strikingly, the emergent self-duality leads to an emergent symmetry and
manifests at these first-order critical points. This discovery is reminiscent
of self-duality protected multicritical points and provides the example of the
critical line with generalized symmetry. Our work has far-reaching implications
for ongoing experimental efforts in Rydberg atom quantum simulators.Comment: 5 + 10 pages, 9 figures. Any comments or suggestions are welcome
Superconductivity from Doping Symmetric Mass Generation Insulators: Application to LaNiO under Pressure
We investigate the bilayer nickelates as a platform to realize the symmetric
mass generation (SMG) insulator, a featureless Mott insulator that arises due
to the Lieb-Schultz-Mattis (LSM) anomaly cancellation in bilayer spin-1/2
lattice systems. Through a single-orbital bilayer square lattice model
involving intralayer hopping and interlayer superexchange interaction ,
we demonstrate the emergence of high-temperature superconductivity (SC) upon
doping the SMG insulator. The SC phase features -wave interlayer
spin-singlet pairing and exhibits a crossover between the BCS and BEC limits by
tuning the ratio. We estimate the SC transition temperature from
both the weak and strong coupling limits at the mean-field level. Our findings
offer insights into the experimentally observed decrease in with pressure
and the strange metal behavior above . Additionally, we propose that both
Ni and orbitals can exhibit superconductivity in
LaNiO under pressure, but their should vary in opposite ways
under doping. This characteristic difference suggests a potential experimental
pathway to identify which electronic orbital plays the principal role in the
formation of superconductivity in this system.Comment: 11 pages, 5 figures, 2 table
Streaming CTR Prediction: Rethinking Recommendation Task for Real-World Streaming Data
The Click-Through Rate (CTR) prediction task is critical in industrial
recommender systems, where models are usually deployed on dynamic streaming
data in practical applications. Such streaming data in real-world recommender
systems face many challenges, such as distribution shift, temporal
non-stationarity, and systematic biases, which bring difficulties to the
training and utilizing of recommendation models. However, most existing studies
approach the CTR prediction as a classification task on static datasets,
assuming that the train and test sets are independent and identically
distributed (a.k.a, i.i.d. assumption). To bridge this gap, we formulate the
CTR prediction problem in streaming scenarios as a Streaming CTR Prediction
task. Accordingly, we propose dedicated benchmark settings and metrics to
evaluate and analyze the performance of the models in streaming data. To better
understand the differences compared to traditional CTR prediction tasks, we
delve into the factors that may affect the model performance, such as parameter
scale, normalization, regularization, etc. The results reveal the existence of
the ''streaming learning dilemma'', whereby the same factor may have different
effects on model performance in the static and streaming scenarios. Based on
the findings, we propose two simple but inspiring methods (i.e., tuning key
parameters and exemplar replay) that significantly improve the effectiveness of
the CTR models in the new streaming scenario. We hope our work will inspire
further research on streaming CTR prediction and help improve the robustness
and adaptability of recommender systems
- …